Data collected in the present study will be used to test the major methods of diagnosing the behavior disorder that has been called child hyperactivity (HK), attention deficit disorder (ADD), and minimal brain dysfunction (MDB). Among the methods to be tested are: (1) the DSM-III method, which divides children with attention deficits into those with and those without hyperactivity; (2) the Hyperactivity/Aggression model, which divides hyperactive children into those with and those without aggression; (3) the Situational method, which compares children with trait hyperactivity (that displayed both at home and at school) and children with situational hyperactivity (that displayed either at home or at school); (4) the Environmental model, which considers environmental-etiological variables such as parenting style, socioeconomic status, and family stability in forming diagnostic groupings; and (5) the Learning Disabilities model, which compares hyperactive children who have learning deficits with hyperactive children who do not have learning deficits. We will also estimate the diagnostic value of other important symptoms, such as impulsivity; of temporal factors, such as age at onset and duration of problem; and of such nonsymptom factors as cognitive functioning. Attempts will be made to identify additional and more precise bases for diagnostic subgrouping by using such methods as: (1) cluster analyses of sets of symptom and backgroung variables; (2) discriminant function analyses between a specific diagnostic group and normal classmates, or across several diagnostic groups; (3) factor analyses to reduce groups of single-source variables to a smaller set of relatively independent dimensions; and (4) multiple regression analyses to identify predictors of important treatment response and adolescent outcome variables.